Sensory control of the initiation of hatching in chicks: effects of a local anesthetic injected into the neck.

Previous work shows that folding a posthatching chick into the hatching position results in the re-initiation of hatching. Furthermore, bending the neck to the right or left serves as a selective signal for turning on hatching behavior. The present study addresses the issue of whether sensory receptors located in the neck provide this signal. Three groups of chicks were folded into the hatching position and placed in glass eggs. In the experimental group, sensory input from the neck was eliminated with a local anesthetic, lidocaine. In these chicks, hatching was initiated only after a long latency, correlated with the time at which the anesthetic wore off. In the two control groups, in which saline was injected into the neck or lidocaine was injected into the thigh, the latency was much shorter. Therefore sensory receptors located in the neck appear to provide input that serves as a selective signal for initiating hatching.